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Image Prod & Eval > Chapter 11 - midterm > Flashcards

Chapter 11 - midterm Flashcards

1
Q

What are the two parts an x-ray beam is divided into?

A
  • Primary Beam
  • Remnant beam
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2
Q

What is the primary beam?

A

The beam that comes out of the tube prior to an interaction with the patient

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3
Q

What is the remnant beam?

A

The radiation coming out of the patient and hitting the IR

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4
Q

What is a general rule for most radiation entering a patient?

A

It never makes it out

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5
Q

How does the remnant beam work?

A

It is the image forming beam that carries the signal from the tissues to the IR

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6
Q

What percentage of the primary beam makes it through the patients?

A

1%

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7
Q

What does the remnant beam contain?

A

Photons from the primary beam, secondary radiation and scattered radiation

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8
Q

What is secondary radiation?

A

Radiation produced by interaction between the primary beam and matter

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9
Q

What is scatter radiation?

A

A type of secondary radiation where the beam spreads in a different direction from where the beam interacts with matter

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10
Q

What does scatter provide in a diagnostic image?

A

Radiographic Fog and unwanted information that can degrade the overall image

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11
Q

What direction does a primary beam come out of a tube?

A

In an upside down fan of diverging rays

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12
Q

In what manner do the rays diverge?

A

They diverge isotropically - in all directions

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13
Q

Where do the xray beams diverge from and where to?

A

Diverge from the focal spot to the object

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14
Q

Which rays do not diverge from the focal spot?

A

The central ray

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15
Q

What position does the central ray follow when leaving the tube?

A

Perpendicular to the IR

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16
Q

What are the 3 important distances in xray?

A

SID, SOD and OID

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17
Q

What is SID?

A

Source to image distance from the FS to the IR

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18
Q

What is SOD?

A

Source to object distance from the FS to the top surface of the part

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19
Q

What is OID?

A

Image distance from the object to the IR

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20
Q

What effects do these distances have on the image?

A

Effect image distortion and spatial resolution

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21
Q

Why is the central ray important in radiography?

A

Its used when positioning the patient

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22
Q

What effect do all other rays have on images?

A

They distort the anatomy to different degrees

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23
Q

Which beam is the point of least divergence?

A

The CR (central ray)

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24
Q

What are the three types of IR?

A
  • Film cassettes
  • Computed Radiography Cassettes (CR)
  • Direct Digital Radiography (DR) flat panel detector
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25
Q

What are the 6 categories of radiographic variables?

A
  • Technical variables
  • Geometrical variables
  • Patient status
  • Image receptor systems
  • Image processing
  • Viewing conditions
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26
Q

What are technical variables?

A

Electrical values set by the radiologist technologist

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27
Q

What are the types of technical variables?

A
  • KvP
  • mAs
  • generator type
  • exposure time
  • filtration
  • collimation
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28
Q

What are geometrical variables?

A

SID, OID, SOD, the angle of the tube to the part and the size of the focal spot

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29
Q

What effect do geometrical variables have on the image?

A

Effect image resolution (i.e. spatial resolution (detail), magnification and distortion)

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30
Q

What is patient status when it relates to radiographic variables?

A

The condition of the patient, status of the disease, age and trauma

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31
Q

What are image receptor systems when they refer to radiographic variables?

A

Anything that interacts with the remnant beam (radiographic grid, table top and IR type)

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32
Q

How can image receptor systems affect image outcome?

A

All can affect the overall resolution

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33
Q

What is image processing as it pertains to radiographic variables?

A

The processing of images utilizing different mathematical algorithms that vary.

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34
Q

What additional image processing techniques affect radiographic variables?

A

The storage, transfer and altering of images through post-processing techniques

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35
Q

What viewing conditions affect radiographic variables?

A

Images are viewed on monitors and ambient light and type of monitor can affect diagnosis

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36
Q

What are the 3 x-ray interactions with tissue?

A
  • Photoelectric interaction
  • Compton scattering
  • Coherent scattering
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37
Q

What is a rare xray interaction with tissue?

A

Characteristics

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38
Q

How does photoelectric effect work?

A

A x-ray photon interacts with an inner shell electron, transfers all of its energy to the electron which ejects it

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39
Q

What is the ejected electron called in photoelectric effect?

A

Photoelectron

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40
Q

What does the photoelectron go on to create?

A

Secondary radiation in the body

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41
Q

What effect does PE have on images?

A

Play a major role in the subject contrast

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42
Q

How do areas on the image appear when no radiation is received on the IR?

A

They appear white or very light gray

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43
Q

What is an energy requirement of the incoming photon in PE?

A

Energy of the incoming photon needs to be just above the binging energy of the inner shell electron

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44
Q

What is the energy formula for PE?

A

Ep= Eb + Eke
- Ep is energy of incoming electron
- Eb is the binding energy of orbital electron
- Eke is the energy of the ejected electron

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45
Q

How is PE related to dose?

A

PE yields most of the patient dose in a given radiograph

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46
Q

What are alternate names for Compton interaction?

A

Modified scattering and Incoherent scattering

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47
Q

How does Compton scattering work?

A

An incoming Xray interacts with an outer shell electron, partially transfers its energy to the electron, which ejects the electron and creates a new x-ray photon at a different angle

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48
Q

What is the ejected electron called in Compton scattering?

A

Recoil electron

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49
Q

How does the wavelength change between incoming photon and new photon in Compton scattering?

A

Small wavelength to longer wavelength (More energy to less energy)

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50
Q

What is the energy formula for Compton scattering?

A

Ep= Es + Eb + Eke
- Ep is energy of incoming electron
- Es is the energy of the scattered xray
- Eb is the binding energy of orbital electron
- Eke is the energy of the ejected electron

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51
Q

In a patient how many compton interactions per photon are standard?

A

A single photon can cause a series of compton interaction, each with a new photon of less energy, eventually ending in PE effect and absorption

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52
Q

What percentage of scatter is compton?

A

97%

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53
Q

What direction does scatter occur in?

A

Occurs in all directions

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54
Q

What is the angle of scatter based on?

A

The original energy of the incoming photon

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55
Q

What is scatter called that comes back towards the tube?

A

Back scatter

56
Q

What direction do scattered xrays that retain most of their energy move in?

A

Move in a forward direction close to that of the original

57
Q

What direction do scattered xrays that retain 84% of their energy move in?

A

Move at a right angle

58
Q

What direction do scattered xrays that retain 68% of their energy move in?

A

Move in a backwards direction (back scatter)

59
Q

What direction do more xrays scatter in and why?

A

Back scatter because most scattered photons have low energy

60
Q

How does kVp effect the probability of scatter?

A

kVp increases the energy of the initial photon, and as energy increases so does the probability of scatter

61
Q

What does scatter produce when it hits the IR?

A

Radiographic fog, aka noise

62
Q

What is the effect of fog on an image?

A

Obscures details within the image

63
Q

How does coherent scattering work?

A

A low level xray photon interacts with a tightly bound electron, transfers all its energy but only excites the electron to release new photon of same energy at slightly different angle

64
Q

What percent of scatter is caused by coherent scatter?

A

3%

65
Q

What effect does coherent scatter have on the image?

A

Very little effect

66
Q

How does the wavelength change between incoming photon and new photon in Coherent scattering?

A

It doesn’t they stay the same size

67
Q

When does characteristic radiation occur?

A

After an ionizing event in a tissue like compton or photoelectric interaction

68
Q

How does characteristic radiation work?

A

An electron is pulled from an outer shell to fill a vacancy in an inner shell

69
Q

What is the result of characteristic radiation?

A

An extremely low photon or UV light

70
Q

Does characteristic radiation have an effect on the xray image?

A

No it has no effect

71
Q

What is attenuation?

A

The partial absorption of the xray in the patient’s body based on thickness and atomic density

72
Q

What is the basis of contrast in an image?

A

Attenuation

73
Q

What does contrast provide in images?

A

Differences between tissues and potential pathology

74
Q

In a homogenous object what is attenuation of the beam based on?

A

The thickness of the tissue

75
Q

How much attenuation occurs in thinner object?

A

Less attenuation and more penetration

76
Q

How much attenuation occurs in thicker objects?

A

More attenuation and less penetration

77
Q

How would a less attenuated object show on a radiograph?

A

Would appear darker on a radiograph

78
Q

How would a more attenuated object appear on a radiograph?

A

Would appear lighted on a radiograph

79
Q

How much is the intensity of the beam cut for every 4-5 cm of tissue?

A

Beam is cut in half

80
Q

How would the exposure technique need to be adjusted for each increase of 4-5 cm?

A

Exposure technique would need to be doubled

81
Q

How would you double the exposure technique?

A

Double the mAs or increase kVP by 15%

82
Q

What rate does attenuation occur for 4-5 cm of tissue?

A

Attenuation occurs at a rate of 50% for every 4-5 cm

83
Q

What factors contribute to the attenuation of the beam at different degrees?

A

The avg Z# and the tissue thickness

84
Q

How are different degrees of attenuation represented in an image?

A

Represented as different shades of gray

85
Q

What do the various shades of gray become part of in an image?

A

Become part of the gray scale of an image

86
Q

What types of interactions result in attenuation?

A

Photoelectric effect and compton scattering

87
Q

What type of interaction does photoelectric effect result in?

A

Absorption

88
Q

What type of interaction does compton effect result in?

A

Scattering

89
Q

What is the end result of the photon in photoelectric effect?

A

X-ray photon disappears

90
Q

What is the end result of the photon in compton effect?

A

Xray photon loses energy and changes direction

91
Q

What does digital imaging rely on?

A

Atomic interactions between the remnant beam and the phosphors of image receptors

92
Q

What is another name for photoelectric interaction?

A

Photoelectric absorption

93
Q

What happens to the photon in photoelectric?

A

It is completely absorbed

94
Q

Where does the interaction occur in photoelectric?

A

Inner shell electron

95
Q

What is the general rule of binding energy for photoelectic?

A

Energy must be slightly higher

96
Q

What happens to the electron in photoelectric?

A

The photon gets ejected as a photoelectron

97
Q

What effect does photoelectric have on contrast?

A

Creates the majority of subject contrast in the image

98
Q

What is another name for compton interaction?

A

Modified or incoherent

99
Q

What happens to the photon in compton interaction?

A

Loses a small amount of energy and changes direction, with the angle based on initial energy

100
Q

Where does the interaction occur in compton?

A

In outer shell electrons

101
Q

What is the general rule of binding energy for compton?

A

Equal but generally much higher

102
Q

What happens to the electron in compton?

A

Recoil electron

103
Q

What effect does compton have on contrast?

A

Can be in the remnant beam but reduces contrast

104
Q

What dose is represented by compton?

A

Occupational dose because of the scatter

105
Q

What is another name for coherent scattering?

A

Unmodified or Thompson

106
Q

What happens to the photon in coherent scattering?

A

Initial photon is absorbed by orbital electrons, which causes excitation. A new photon is created and travels at a slightly different angle and possesses the same energy as the initial photon

107
Q

Where does the interaction occur in coherent scattering?

A

Orbital electron

108
Q

What is the general rule of binding energy for coherent scattering?

A

Less energy causing the electron to be excited

109
Q

What happens to the electron as part of coherent scattering?

A

Nothing, it gets excited but there is no ionization

110
Q

What effect does coherent scattering have on image contrast?

A

Little to no effect as only 3% makes it to the IR

111
Q

What is a Rayleigh interaction?

A

A variation of coherent scattering

112
Q

What happens to the photon in Rayleigh interaction?

A

Initial photon is absorbed by entire atom, and a new photon is created at the same energy but at different angle

113
Q

Where does Rayleigh interaction take place?

A

Entire atom is excited

114
Q

When does characteristic interaction occur?

A

After an atom is ionized by either PE or compton

115
Q

Where does characteristic interaction take place?

A

In any shell with an electron vacancy

116
Q

What happens to the electron as part of characteristic interaction?

A

Electron falls into an inner shell vacancy which causes a loss of potential energy and emission

117
Q

What effect does characteristic interaction have on image contrast?

A

Energy created is so low it has no effect on the image and is likely to be light or UV radiation

118
Q

What happens to the object in an image when the tube is angled?

A

The objects are going to be elongated and stretched

119
Q

What are some ways to reduce scatter?

A

Reduce kVp, reduce patient size, utilize grids

120
Q

Who/what is compton scatter bad for?

A

The image because it creates noise, the patient because it causes ionization, and anyone in the room bc it leaves the patient

121
Q

What does low contrast mean?

A

The ability to distinguish small differences in absorption levels between one object and another

122
Q

What is long scale contrast?

A

Many different greys in a scale with small differences in each color

123
Q

What is short scale contrast?

A

Not many differences between greys

124
Q

How is a longer scale benefitial to imaging?

A

The longer the scale the more greys are represented and more tissues types you can potentially see

125
Q

How is contrast defined?

A

The ability to distinguish small attenuation differences between tissues as manifested in different gray scales

126
Q

What is the relationship between wavelength and energy?

A

Indirectly proportional

127
Q

What type of wavelength do low energy photons have?

A

Long wavelengths

128
Q

What type of wavelength do medium energy photons have?

A

Shorter wavelengths that interact with electrons and cause ionization

129
Q

What type of wavelength do high energy photons have?

A

Very short wavelength that disappear when they interact with a nucleus

130
Q

What is the effective atomic number of fat?

A

6.3

131
Q

What is the effective atomic # of bone?

A

13.8

132
Q

Where will greater absorption occur between bone and fat?

A

In bone because of the higher atomic number

133
Q

What are the other 2 types of interactions that are not used in diagnostic imaging?

A

Pair Production and Photodisintegration

134
Q

How does pair production work?

A

X-ray photons with 1.02 MeV interact with the nuclear field of an atom, which causes the photon to disappear producing a positron and negatron

135
Q

What happens to the Positron in Pair production?

A

It interacts with an electron and annhilates it, producing two photons of .5 MeV energy each

136
Q

How does photodisintigration work?

A

xray photons with energy over 10 Mev get completely absorbed into the nucleus making it explode producing nuclear fragments

Image Prod & Eval (10 decks)

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